The cardiac glycosides and the sympathomimetic amines are the principal inotropic agents used in the management of congestive heart failure. Although the cardiac glycosides, especially digitalis, are among the most frequently prescribed drugs, they have numerous liabilities such as a low therapeutic index and erratic absorption, and are associated with life-threatening arrhythmias and deleterious drug-drug interactions. In addition, many patients either do not respond, or become refractory to these agents. The sympathomimetic amines, such as dopamine and epinephrine, have limited utility due to positive chronotropic effects, arrhythmogenic properties, and oral ineffectiveness.
More recently, new classes of inotropic agents have been found. These include certain dihydropyridazinone derivatives such as those taught in U.S. Pat. Nos. 4,353,905, 4,361,563, 4,304,777, and 4,404,203 which cause an increase in myocardial contractility in anesthetized dogs and cats. Other pyridazinone derivatives are taught in the art to be cardiotonics, antihypertensives, and antithrombotic agents; see, e.g., U.S. Pat. No. 4,258,185.
The present invention provides certain pyridazinone derivatives which are potent, long-acting, orally effective positive inotropic agents which cause minimal effects on blood pressure and heart rate.